Grand Rapids was 3-4 inches of rain from disaster

Sunday, April 28, 2013

GRAND RAPIDS (AP) — The swollen Grand River came uncomfortably close to breaching its flood walls and causing disastrous flooding in Grand Rapids earlier this month, a National Weather Service hydrologist said.

Flooding forced an estimated 1,700 people from the Grand Rapids area to head to higher ground.

With the river already rising, an April 19 storm was forecast to dump 1 to 2 inches of rain, but only about one-third of an inch materialized.

An extra 3 to 4 inches of rain likely would have been enough to bring the water up against the bottoms of downtown bridges and force it up against flood walls in the city of 188,000, weather service hydrologist Mark Walton told MLive.com.

“Once it gets into the bridges, who knows what would have happened?” Walton said. “We were very close to putting us to the limit. ... Three or 4 inches ... that would have done it.”

Walton said a “game changer” happened when the April 19 rain fell short of the forecast.

The Grand River reached a record 21.85 feet, or 3.85 feet above flood stage last Monday. But it never approached the record flow rate of 109 years before, Walton said.

A 1904 flood had water traveling through a downtown stretch of the river at 54,000 cubic feet per second, Walton said. Back then, the flood walls hadn’t been built, meaning the water spread farther but didn’t rise as high. The volume last week measured 35,000 cubic feet per second.

The chances that Michigan’s second-largest city will experience another flood like this year’s are about a 6 percent each year, Walton said. That means it happens about once every 16 years.

On Sunday, the Grand River at Grand Rapids was at 14.9 feet, 3.1 feet below flood stage, and falling, according to the weather service.

The river remained over flood stage at two other spots Sunday. Just upstream from Grand Rapids, it stood at 12.9 feet, or 0.9 feet over, at Comstock Park in Kent County’s Plainfield Township. The river level was 14 feet, or 0.7 feet over flood stage, in Ottawa County’s Robinson Township.